Self-Sacrificial Growth of Heterojunction Photocatalytic Fibers as a Humidity-Adaptive Platform for Sustainable VOC Purification

We report self-sacrificial in situ synthesis of a Z-scheme heterojunction photocatalyst Fe₃(PO₄)₂/MIL–88B(Fe)–NH₂ that shares a common metal component, where the Fe fiber substrate serves dually as the structural support and metal precursor. The resulting heterojunction fiber composite, noted as Fe/MIL–NH₂@fiber, demonstrates efficient charge separation and reactive oxygen species (ROS) generation, in which MIL–88B(Fe)–NH₂ drives superoxide radical (·O2-) formation while Fe₃(PO₄)₂ contributes to hydroxyl radical (·OH⁻) production. This study primarily focuses on the removal of formaldehyde (HCHO) as a model volatile organic compound (VOC) to explore how the developed Fe/MIL–NH₂@fiber platform achieves a humidity-adaptive removal process. Fe/MIL–NH₂@fiber exhibits notable performance in HCHO removal through a synergistic process of adsorption and photodegradation. Humidity plays a crucial role in mediating the interactions between the porous photocatalyst and HCHO, where excessive relative humidity (90% RH) suppresses adsorption but simultaneously enhances photodegradation by facilitating ·OH⁻ generation. Kinetic analyses reveal that adsorption proceeds faster than photodegradation, suggesting that the metal–organic framework (MOF)-integrated heterojunction is an advantageous solution for VOC removal, benefiting from a dual-action mechanism where immediate capture is complemented by permanent oxidative removal. Notably, the developed Fe/MIL–NH₂@fiber demonstrated a removal efficiency greater than 85% after three consecutive cycles, highlighting its robustness and potential for long-term applications under varying humidity conditions. This work offers design principles applicable to MOF-integrated photocatalysts for step-forward air purification in practical scenarios.